The long term goal of this proposal is the development of biologically sensitive, selective and reliable electrochemical devices for the determination of metabolites of physiological relevance. At the research level, these devices can be used to study the relationship between periodic fluctuations of metabolites and the development of disorders in the human body. At the application level, the development of these devices can result in the decentralization of clinical laboratories by providing the physicians and ambulatory patients a fast, reliable, easy and low cost way of analyzing for metabolites. To achieve this goal it is necessary to understand the interfacial dynamics of electron transfer reactions of redox enzymes. What variables control the electron transfer reaction between a redox enzyme and an electrode surface? In the presence of redox mediators how fast is the electron transfer reaction between the enzyme and the mediator? What variables allow its control? We propose to continue our efforts toward the discovery of potentially useful redox mediators. We also propose to study the electron transfer reaction between these redox mediators and several redox enzymes. The enzymatic systems to be studied are oxidases such as lactate, choline and cholesterol and dehydrogenases such as malate and glycerol. Redox mediators to be tested are conductive polymers, organic metals and transition metal complexes. Electrochemical and spectroscopical techniques such as UV-Vis, Cyclic and Rotating Disk Voltammetry, Bulk Electrolysis and Spectro-electrochemistry will be used to study how variables such as pH, ionic strength, the concentration of the enzyme, cofactor, substrate and mediator and the presence of metal ions affect the kinetics and thermodynamics of these redox reactions.